U.S. Pat. No. 3,953,638 which issued to Clifford B. Kemp on Apr. 27, 1976 discloses a Multi-Ply Absorbent Wiping Product Having Relatively Inextensible Center Ply Bonded Tp Highly Extensible Outer Plies, and concomitant methods. Such a product is stated to have superior caliper and bulk impresson when wet due to the fact that the unadhered areas of the extensible outer plies expand in the Z-direction (i.e., out of the plane of the paper) when the structure becomes wetted. That is, in such a product wherein the extensible outer plies are creped tissue paper, wetting causes crepe induced stresses to be relieved. Were the outer plies not constrained by the relatively inextensible center ply they would become elongated in the plane of the paper when wetted. However, being so constrained by a relatively inextensible center ply, the extensible outer plies expand outwardly (i.e., pucker in the Z-direction of the product) when the product is wetted. Such paper has, however, low tensile energy absorption relative to embodiments of the present invention, all other things being equal, and does not have a monomodal stress/strain character as do preferred embodiments of the present invention as is discussed in greater detail hereinafter.
U.S. Pat. No. 3,615,976 which issued to Dan D. Endres et al on Oct. 26, 1971 discloses a Method of Producing a High Bulk Macrocrepe Product which, during its manufacture, is dampened to effect puckering of creped wadding to precipitate macrocrepe and then dried to preserve the macrocrepe. The creped wadding is secured by adhesive in well spaced zones to a drawn synthetic fiber web which is substantially unaffected by the dampening.
U.S. Pat. No. 3,650,882 which issued to Gordon D. Thomas on Mar. 21, 1972 discloses a Multi-Ply Paper Towel having an elastically extensible inner ply of creped tissue disposed between less extensible, embossed outer plies.
U.S. Pat. No. 4,100,017 which issued to Thomas Joseph Flautt, Jr. on July 11, 1978 discloses a Multi-Ply Tissue Product wherein, for example, plies of dissimilar creping characteristics are juxtaposed with less resultant caliper loss than normally precipitated by juxtaposing similarly creped plies.
U.S. Pat. No. 3,544,420 which issued to James A. Murphy et al on Dec. 1, 1970 discloses a Creped Tissue Product comprising bias oriented plies. The product is stated to be extensible in both the longitudinal and transverse directions and is said to have unusually good strength and resistance to bursting, particularly in the transverse direction albeit, preferably, the plies are identically creped.
U.S. Pat. No. 4,072,557 which issued to Christian Schiel on Feb. 7, 1978 discloses a Method And Apparatus For Shrinking A Traveling Web Of Fibrous Material which entails a differential velocity transfer of a paper web in the wet-end of a papermaking machine to effect shrinking (i.e., wet-foreshortening of the web). Wet-foreshortened paper is also disclosed in British Pat. No. 1,212,473 which was published Nov. 18, 1970 and in Canadian Pat. No. 879,436 which issued Aug. 31, 1971; and both of which patents were derived from Finnish Pat. Application No. 561/68 which has a priority date of Mar. 1, 1968.
As compared to the background art, the present invention provides a highly absorbent multi-ply tissue product wherein extensible plies having substantial individual tensile strengths but sufficiently different stress/strain properties or stress/strain characters to synergistically interact to effect high wet bulk and liquid absorbency; and high tensile energy absorption. Preferably, the plies have sufficiently matched elongation properties that their tensile strengths are additive throughout the stress/strain domain of the product which product is accordingly characterized by a monomodal stress/strain property. A monomodal stess/strain property for such a multi-ply tissue paper product is hereby defined as a stress/strain curve having a single peak whereat all of the plies rupture virtually simultaneously as compared to a bimodal or multi-modal stress/strain property for two-ply or multi-ply products, respectively, which results from individual plies rupturing at different strain values.